The invention pertains to a circuit arrangement for providing a stable output voltage and/or output current from an input voltage which is variable over a wide range and might also assume exceptionally low values from case to case, and as a possible application of such circuit, a redundancy module having active decoupling components.
In systems and automation engineering, as well as in other fields of electronics, one usually employs internal supply voltages of about 3V to about 60V. Internal supply voltages are those voltages which are required by the electrical consumers which are connected to the internal supply network of the respective apparatus or the respective system, for their proper functioning and which are provided by one or more current supply unit(s), which is (are) also connected to the internal supply network.
The energy supply capabilities of such current supply units are limited in any case. In the case of an overload or a short circuit on the supply lines, the supply voltages, which are provided by the connected current supply unit(s), will drop in accordance with their overload characteristics; in the case of a short circuit, oftentimes to values below 1V. At drops of the supply voltage below certain values, which differ depending on the consumer, some consumers will turn off in a controlled manner, other consumers will stop functioning properly at first and will cease functioning completely only at a further decrease of the voltage supply. In case of a short circuit, at voltages below 1V, none of the usual/known (designed for nominal voltages of 3V or above) consumers continue functioning.
For increasing the reliability for critical applications, multiple current supply units are often connected in parallel/redundantly, in order to be able to ensure the supply of the connected consumers and, in this manner, of the entire apparatus resp. the entire system, even in case of a failure of one (or single) current supply unit(s). In doing so, depending on the reliability requirements of the apparatuses resp. systems, at least two, but often also more current supply units are connected together by means of so called redundancy modules.
The redundancy modules include an output stage, which, in case of an unbalance (i.e. unequally high output voltages of the feeding current supply units) or in case of a failure of one (or single) connected current supply unit(s), prevents a current return flow from the normally functioning current supply unit(s) into the current supply unit, which is defective or has an undervoltage, and which also can completely disconnect defective current supply units from the consumers in case of a disturbance or a short circuit. In the simplest case such output stage is realized by a diode. For reasons of energy efficiency, but often also for thermal reasons, it is sensible or necessary to realize such output stages with active semiconductor components instead of simple diodes. Circuits with active semiconductor components require a sufficiently high supply voltage, which, for proper functioning, often also needs to be sufficiently stable within limits.
Such supply voltage is neither available in case of an overload or a short circuit on the supply line(s) nor in case of disturbances of the feeding current supply unit(s).
If the proper functioning of the redundancy modules or other critical consumers, (e.g. monitoring and signalling units), which are connected to the internal supply network, is required also in case of such fault, the supply voltage, which is required by them, can be provided by independent current supplies, such as a) additional current supply units having separate supply lines for the case of a fault, b) batteries/accumulators, c) electrolytic capacitor buffer circuits (usually having so-called “gold-caps”), d) solar cells or also e) recent methods of energy harvesting. The aforementioned solutions have the disadvantage that they either require a) comparably elaborate additional electronics and, in addition to this, additional cabling or b) regular maintenance. In case of c), the functionality is limited to a short period of time and in the case of d), to certain environmental conditions. Furthermore, the solutions c), d) and especially e) are limited in their energy supply capabilities and thus cannot be employed in many cases.
For the mentioned failure case, in which the supply voltage, due to an overload or a short circuit, drops below its nominal value, two variants of failure cases are to be distinguished: case a) overload or short circuit already at the time of turning on; in this case the supply voltage never attains its nominal value or at least a voltage value which can be used by the connected consumers—and case b) overload or short circuit from within the normal operation; in this case the supply voltage drops more or less rapidly to values which are invalidly low for the connected consumers.
If one tries, on the basis of known circuits for supplying consumers from very small voltages, to find a solution, which is suitable for both preceding cases at the same time, the same problems arise again and again. Circuits, which are suitable to, from very small input voltages such as 1V and smaller, generate output voltages for common consumers in the amount of about 3V to about 60V, cannot handle, at the same inputs, at which, as laid out, the very small source voltages are applied, as an alternative operating case, also high voltages of 20V . . . 40V . . . 60V. These circuits are furthermore generally only laid out for smaller currents than about 1 A and smaller voltages than about 20V—in any case not suitable to fulfil all requirements with regard to the input voltage stability, output voltage stability and the current supply capability at the same time, without adding a considerable amount of additional electronics.